In a radio frequency (RF) environment, interference signals may have jamming effects on an RF receiving system. Jamming interference signals may originate, for example, in a laptop computer on an airplane, a radio or television tower, or any high frequency device such as radar, a radio or cellular telephone. Also jamming signals may be generated by individuals, such as a combatant in a military or other environment.
Frequency selective limiters (FSLs), also known as power selective limiters (PSLs), are used for suppressing RF signals in various types of equipment having a need for protection against interference and jamming signals. FSLs are attenuating devices that may attenuate higher power level signals, such as interference and jamming signals, while simultaneously allowing lower power level signals separated by only a small frequency offset from the higher level signals to pass with relatively low loss.
FSLs have particular applicability in RF systems used, for example, for navigational purposes and, more particularly, to receivers which operate in satellite navigation systems such as the well known Global Positioning System (GPS). For example, FSLs can be used in electronic warfare systems ahead of a Bragg cell or a compressive receiver, or other broadband receiver technology, with modest dynamic range, to limit the input signal power so that the receiver is operated in a linear manner. Non-linearities in broadband receivers can cause inter-modulation between multiple input frequencies that produce spurious signals, which can obscure the signals of interest. Stripline FSLs fabricated with yttrium iron garnet (YIG) films have been developed for this application and rely on the non-linear excitation of spin waves in the YIG film to achieve the desired frequency selective limiting behavior. FSLs have also been proposed to improve the “anti-jam” performance of GPS receivers and improve the signal to noise ratio of satellite TV receivers. Thus, FSLs are used to eliminate unwanted interference or jamming signals.